Issue #1816582 by klausi, Crell: Fixed Fatal error in exception handler on 405 HTML responses.

core/lib/Drupal/Core/ExceptionController.php

@@ -86,7 +86,7 @@ public function execute(FlattenException $exception, Request $request) {
    *   The request object that triggered this exception.
    */
   public function on405Html(FlattenException $exception, Request $request) {
-    $event->setResponse(new Response('Method Not Allowed', 405));
+    return new Response('Method Not Allowed', 405);
   }
 
   /**

core/modules/system/lib/Drupal/system/Tests/System/ExceptionControllerTest.php

+<?php
+
+/**
+ * Definition of Drupal\system\Tests\System\ExceptionControllerTest.
+ */
+
+namespace Drupal\system\Tests\System;
+
+use \Drupal\Core\ContentNegotiation;
+use \Drupal\Core\ExceptionController;
+use \Drupal\simpletest\UnitTestBase;
+use \Symfony\Component\HttpFoundation\Request;
+use \Symfony\Component\HttpKernel\Exception\FlattenException;
+
+/**
+ * Tests exception controller.
+ */
+class ExceptionControllerTest extends UnitTestBase {
+
+  public static function getInfo() {
+    return array(
+      'name' => 'Exception controller',
+      'description' => 'Performs tests on the exception handler controller class.',
+      'group' => 'System',
+    );
+  }
+
+  /**
+   * Ensure the execute() method returns a valid response on 405 exceptions.
+   */
+  public function test405HTML() {
+    $exception = new \Exception('Test exception');
+    $flat_exception = FlattenException::create($exception, 405);
+    $exception_controller = new ExceptionController(new ContentNegotiation());
+    $response = $exception_controller->execute($flat_exception, new Request());
+    $this->assertEqual($response->getStatusCode(), 405, 'HTTP status of response is correct.');
+    $this->assertEqual($response->getContent(), 'Method Not Allowed', 'HTTP response body is correct.');
+  }
+}